1. Field of the Invention
The present invention relates to a grinding wheel for mirror finishing, and especially, to a grindstone containing fine abrasives for finishing optical glass, semiconductor substrates or the like.
2. Prior Art
Processes for machining a surface of work to a mirror finish generally include honing, super-finishing, lapping, grinding with coated abrasives, polishing, buffing and so on. Honing and super-finishing use a grinding wheel similar to a normal grinding wheel, but are superior in working efficiency. The reason is as follows: Sharp grinding is always conducted due to fracture of abrasive grain which comes from the high speed of vibration of the grinding wheel and the frequent changes of the directions of these vibrations. Also, the efficiency of the honing operation depends upon the performance of sharp grinding due to fracture of abrasive grain. Lapping is a finishing process for the surface of the work to be machined as a cutting tool, which is used for highly accurate dimension and fine surface. The grinding process with the coated abrasive aims only for finishing the surface of the work to be machined without questioning accuracy of dimensions.
As mentioned above, on the machining in which high accuracy of finishing is required, for example, surface finishing for lenses of cameras, microscopes, etc., lapping is the process of choice. However, this process has its drawback in taking much time in lapping. The finishing process by grinding wheel is superior in operationability, but its abrasive performance depends on filling ratio of abrasive grain. Accordingly, it has been required to raise the filling ratio of abrasives grain so as to improve the abrasive performance. However there is a practical limit in obtaining the filling ratio of abrasive grains due to the problem of bonding force between the abrasive grains to each other. And therefore, the filling ratio of abrasive grains has been 90% at the most, in practice, thus there is a limit in abrasive performance.